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><H1
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><A
NAME="AEN1079"
>6.6. Formatting</A
></H1
><P
><I
CLASS="GLOSSTERM"
>Formatting</I
> is the process of writing marks 
	on the magnetic media that are used to mark tracks and sectors.
	Before a disk is formatted, its magnetic surface is a complete mess
	of magnetic signals.  When it is formatted, some order is brought
	into the chaos by essentially drawing lines where the tracks go, and
	where they are divided into sectors.  The actual details are not
	quite exactly like this, but that is irrelevant.  What is important
	is that a disk cannot be used unless it has been formatted.</P
><P
>The terminology is a bit confusing here: in MS-DOS and MS 
	Windows, the word formatting is used to cover also the process of
	creating a filesystem (which will be discussed below).  There, the
	two processes are often combined, especially for floppies.  When the
	distinction needs to be made, the real formatting is called
	<I
CLASS="GLOSSTERM"
>low-level formatting</I
>, while making the 
	filesystem is called <I
CLASS="GLOSSTERM"
>high-level formatting</I
>.
	In UNIX circles, the two are called formatting and making a
	filesystem, so that's what is used in this book as well.</P
><P
>For IDE and some SCSI disks the formatting is actually
	done at the factory and doesn't need to be repeated; hence most
	people rarely need to worry about it.  In fact, formatting a hard
	disk can cause it to work less well, for example because a disk
	might need to be formatted in some very special way to
	allow automatic bad sector replacement to work.</P
><P
>Disks that need to be or can be formatted often require a
	special program anyway, because the interface to the formatting
	logic inside the drive is different from drive to drive. The
	formatting program is often either on the controller BIOS, or is
	supplied as an MS-DOS program; neither of these can easily
	be used from within Linux.</P
><P
>During formatting one might encounter bad spots on the
	disk, called <I
CLASS="GLOSSTERM"
>bad blocks</I
> or <I
CLASS="GLOSSTERM"
>bad
	sectors</I
>.  These are sometimes handled by the drive
	itself, but even then, if more of them develop, something needs to
	be done to avoid using those parts of the disk.  The logic to do
	this is built into the filesystem; how to add the information into
	the filesystem is described below.  Alternatively, one might create
	a small partition that covers just the bad part of the disk; this
	approach might be a good idea if the bad spot is very large, since
	filesystems can sometimes have trouble with very large bad areas.</P
><P
>Floppies are formatted with <B
CLASS="COMMAND"
>fdformat</B
>.  The 
	floppy device file to use is given as the parameter.  For example,
	the following command would format a high density, 3.5 inch floppy
	in the first floppy drive:

        <TABLE
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BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><FONT
COLOR="#000000"
><PRE
CLASS="SCREEN"
>	<TT
CLASS="PROMPT"
>$</TT
> <TT
CLASS="USERINPUT"
><B
>fdformat /dev/fd0H1440</B
></TT
>
	<TT
CLASS="COMPUTEROUTPUT"
>Double-sided, 80 tracks, 18 sec/track. Total capacity 
	1440 kB.</TT
>
	<TT
CLASS="COMPUTEROUTPUT"
>Formatting ... done</TT
>
	<TT
CLASS="COMPUTEROUTPUT"
>Verifying ... done</TT
>
	<TT
CLASS="PROMPT"
>$</TT
>
	</PRE
></FONT
></TD
></TR
></TABLE
>

	Note that if you want to use an autodetecting device (e.g.,
	<TT
CLASS="FILENAME"
>/dev/fd0</TT
>), you <EM
>must</EM
> set 
	the parameters of the device with <B
CLASS="COMMAND"
>setfdprm</B
> first.
	To achieve the same effect as above, one would have to do the
	following:

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><TR
><TD
><FONT
COLOR="#000000"
><PRE
CLASS="SCREEN"
>	<TT
CLASS="PROMPT"
>$</TT
> <TT
CLASS="USERINPUT"
><B
>setfdprm /dev/fd0 1440/1440</B
></TT
>
	<TT
CLASS="PROMPT"
>$</TT
> <TT
CLASS="USERINPUT"
><B
>fdformat /dev/fd0</B
></TT
>
	<TT
CLASS="COMPUTEROUTPUT"
>Double-sided, 80 tracks, 18 sec/track. Total capacity 
	1440 kB.</TT
>
	<TT
CLASS="COMPUTEROUTPUT"
>Formatting ... done</TT
>
	<TT
CLASS="COMPUTEROUTPUT"
>Verifying ... done</TT
>
	<TT
CLASS="PROMPT"
>$</TT
>
	</PRE
></FONT
></TD
></TR
></TABLE
>

	It is usually more convenient to choose the correct device file that
	matches the type of the floppy.  Note that it is unwise to format
	floppies to contain more information than what they are
	designed for.</P
><P
><B
CLASS="COMMAND"
>fdformat</B
> will also validate the floppy, 
	i.e., check it for bad blocks.  It will try a bad block several
	times (you can usually hear this, the drive noise changes
	dramatically). If the floppy is only marginally bad (due to dirt on
	the read/write head, some errors are false signals),
	<B
CLASS="COMMAND"
>fdformat</B
> won't complain, but a real error will
	abort the validation process. The kernel will print log messages for
	each I/O error it finds; these will go to the console or, if
	<B
CLASS="COMMAND"
>syslog</B
> is being used, to the file
	<TT
CLASS="FILENAME"
>/usr/log/messages</TT
>.  <B
CLASS="COMMAND"
>fdformat</B
>
	itself won't tell where the error is (one usually doesn't care,
	floppies are cheap enough that a bad one is automatically thrown
	away).

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BORDER="1"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><FONT
COLOR="#000000"
><PRE
CLASS="SCREEN"
>	<TT
CLASS="PROMPT"
>$</TT
> <TT
CLASS="USERINPUT"
><B
>fdformat /dev/fd0H1440</B
></TT
>
	<TT
CLASS="COMPUTEROUTPUT"
>Double-sided, 80 tracks, 18 sec/track. Total capacity 
	1440 kB.</TT
>
	<TT
CLASS="COMPUTEROUTPUT"
>Formatting ... done</TT
>
	<TT
CLASS="COMPUTEROUTPUT"
>Verifying ... read: Unknown error</TT
>
	<TT
CLASS="PROMPT"
>$</TT
>
	</PRE
></FONT
></TD
></TR
></TABLE
>

	The <B
CLASS="COMMAND"
>badblocks</B
> command can be used to search any 
	disk or partition for bad blocks (including a floppy).  It does not
	format the disk, so it can be used to check even existing
	filesystems.  The example below checks a 3.5 inch floppy with two
	bad blocks.

        <TABLE
BORDER="1"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><FONT
COLOR="#000000"
><PRE
CLASS="SCREEN"
>	<TT
CLASS="PROMPT"
>$</TT
> <TT
CLASS="USERINPUT"
><B
>badblocks /dev/fd0H1440 1440</B
></TT
>
	<TT
CLASS="COMPUTEROUTPUT"
>718</TT
>
	<TT
CLASS="COMPUTEROUTPUT"
>719</TT
>
	<TT
CLASS="PROMPT"
>$</TT
>
	</PRE
></FONT
></TD
></TR
></TABLE
>

	<B
CLASS="COMMAND"
>badblocks</B
> outputs the block numbers of the bad
	blocks it finds.  Most filesystems can avoid such bad blocks. They
	maintain a list of known bad blocks, which is initialised when the
	filesystem is made, and can be modified later.	The initial search
	for bad blocks can be done by the <B
CLASS="COMMAND"
>mkfs</B
> command
	(which initialises the filesystem), but later checks should be done
	with <B
CLASS="COMMAND"
>badblocks</B
> and the new blocks should be added
	with <B
CLASS="COMMAND"
>fsck</B
>.	We'll describe
	<B
CLASS="COMMAND"
>mkfs</B
>
	and <B
CLASS="COMMAND"
>fsck</B
> later.</P
><P
>Many modern disks automatically notice bad blocks, and attempt
	to fix them by using a special, reserved good block instead. This is
	invisible to the operating system.  This feature should be
	documented in the disk's manual, if you're curious if it is
	happening.  Even such disks can fail, if the number of bad blocks
	grows too large, although chances are that by then the disk
	will be so rotten as to be unusable.</P
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